1. Field of the Invention
The present invention relates generally to a spread spectrum communication system, and more specifically, to spreading factor estimation in a spread spectrum communication system.
2. Description of the Prior Art
In a spread spectrum system, a modulation technique is used which spreads the information signal over a wide frequency band within the communication channel. The frequency band is much wider than the minimum bandwidth required to carry the information signal. For example, if the information signal is a voice signal, it may have a bandwidth of only a few kilohertz but, during transmission, it's energy could be spread so as to be transmitted over a channel 5 MHz wide. This is accomplished by modulating the information signal with a wideband encoding signal. The information signal is then recovered by remapping the received spread spectrum into its original bandwidth.
Spread spectrum systems can be multiple access communication systems. One type is a code division multiple access (CDMA) system. In a CDMA system, users of the system can simultaneously use the same wideband physical communication channel (for example, the same 5 MHz part of the spectrum) with the signals between one group/pair of users being differentiated from that of another by a unique spreading code.
The present invention is a particularly applicable to a cellular system. A highly schematic cellular architecture is shown in FIG. 1. The system comprises a plurality of macrocell base stations 10 (only an exemplary 10a, 10b, 10c being shown) providing service within a corresponding macrocell 12 (only an exemplary 12a, 12b, 12c being shown). The system also comprises a plurality of mobile stations 14 (only an exemplary 14a and 14b are shown in the macrocell 10a). Each base station 10 communicates with the mobile stations 14 on a CDMA channels at a frequency F1 and a bandwidth of 5 MHz, the communication channel (s) carried out between a base station 10 and a mobile station 14 in the service area thereof being defined by at least one unique spreading code.